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 A239740 a(n) = gcd(Sum_{k=1...n} F(k), Product{j=1...n} F(j)), where F(k) is the k-th Fibonacci number. 2
 1, 1, 2, 1, 6, 20, 3, 18, 8, 143, 8, 8, 21, 986, 84, 63, 220, 6764, 55, 770, 144, 46367, 144, 432, 377, 317810, 16588, 377, 43428, 2178308, 987, 53298, 2584, 14930351, 2584, 18088, 6765, 102334154, 784740, 20295, 2054476, 701408732, 17711, 1664834, 46368 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS The Fibonacci numbers in the sequence are 1, 2, 3, 8, 21, 55, 144, 377, 987, ... and a majority are elements of A001906 (F(2*n)= bisection of Fibonacci sequence). We find consecutive values such that (1, 2), (2, 3), (20, 21), (986, 987), (6764, 6765), (46367, 46368), (317810, 317811), (14930351, 14930352), ... LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..1000 EXAMPLE The first 8 Fibonacci numbers are 1,1,2,3,5,8,13,21 and 1+1+2+3+5+8+13+21 = 54. So a(8) = gcd(54, 1*1*2*3*5*8*13*21) = 18. MAPLE with(combinat, fibonacci):seq(gcd(add(fibonacci(i), i=1..n), mul(fibonacci(j), j=1..n)), n=1..60); MATHEMATICA nn=60; With[{prs=Fibonacci[Range[nn]]}, Table[GCD[Total[Take[prs, n]], Times@@Take[ prs, n]], {n, nn}]] PROG (Haskell) a239740 n = gcd (sum fs) (product fs) where fs = take n \$ tail a000045_list -- Reinhard Zumkeller, Mar 27 2014 CROSSREFS Cf. A000045, A001906. Sequence in context: A101032 A025271 A153804 * A268371 A318918 A100404 Adjacent sequences: A239737 A239738 A239739 * A239741 A239742 A239743 KEYWORD nonn AUTHOR Michel Lagneau, Mar 26 2014 STATUS approved

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Last modified June 9 12:36 EDT 2023. Contains 363178 sequences. (Running on oeis4.)